Box-like blending chamber with barrier elements to produce uniform flow of papermaking stock

ABSTRACT

Apparatus for spreading the flow of papermaking stock so as to establish flow having uniform velocity across the width of a relatively wide conduit, which apparatus includes branch tubes for feeding the flow from a tapered header to the top or bottom wall of a boxlike blending chamber where the streams from the branch tubes impinge against the opposite wall. Barrier elements are disposed in the area of impingement in the blending chamber in a manner whereby they isolate the streams entering the blending chamber from the branch tubes so as to obtain a more uniform velocity profile. The barrier elements which are disposed between the center lines of the adjoining tubes extend between the top and bottom walls, and also extend from a point preceding the upstream side of the branch tubes to a point along the stock flow path through the blending chamber at least beyond the center lines of the branch tubes.

0 llnlted States Patent [151 3,652,391 Spengos et al. [451 Mar. 28, 11972 [54] BOX-LIKE BLENDING CHAMBER WITH BARRIER ELEMENTS To Primary Examiner-S. Leon Bashore.

D Assistant Examiner-R. H. Tushin v 0F AttorneyWilliam J. Foley, Martin .1. Foley, Martin L. Falgus, John W. Kane, Jr. and John A. Weygandt [72] inventors: Aris C. Spengos, Wallingford; Richard B.

Kaiser, Swarthmore, both of Pa. [5 7] ABSTRACT 73 A 2 S a P C d l P Apparatus for spreading the flow of papermaking stock so as ss'gnee co aver ompany 1 a e p la a to establish flow having unifonn velocity across the width of a [22] Filed: Jan. 20, 1970 relatively wide conduit, which apparatus includes branch tubes for feeding the flow from a tapered header to the top or [2 H Appl' 4225 bottom wall of a boxlike blending chamber where the streams from the branch tubes impinge against the opposite wall. Bar- [52] 111.8. Cl ..l62/343, 137/602, 162/216 Tier elements are disposed in the area 0f impingement in [he 51 Int. Cl. .mu l/06 blending chamber in e mehheh' whereby y isolate the [58] Field of Search ..l62/343, 336, 216, 339; Streams entering the blending chamber from the branch tubes 137/602 so as to obtain a more uniform velocity profile. The barrier elements which are disposed between the center lines of the l 56] References Cited adjoining tubes extend between the top and bottom walls, and also extend from a point preceding the upstream side of the UNITED STATES PATENTS branch tubes to a point along the stock flow path through the blending chamber at least beyond the center lines of the 3,298,905 1/1967 Spengos et al ..l62/343 branch tubes 2,281,293 4/1942 Lang ..162/339 3,135,650 6/1964 14 Claims, 3 Drawing Figures Robinson et a1. ..162/343 X PATENTEDMMS I972 INVENTORS. ARIS C. SPENGOS BY RICHARD B. KAISER ATTORNEY.

BOX-LIKE BLENDING CHAMBER WITH BARRIER ELEMENTS TO PRODUCE UNIFORM FLOW OF PAPERMAKING STOCK BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to flow control apparatus and, more particularly, to apparatus for developing fluid flow in a stream into fluid flow having a substantially uniform velocity profile across the width of a relatively wide conduit or channel.

2. Description of the Prior Art In papermaking machines, for example, there is a basic requirement for some means of transforming the flow of stock in a confined pipe into a broad, flat stream moving with uniform velocity across its width so as to produce a paper web having uniform properties, such as basis weight, thickness and strength, when the stock is deposited onto a moving screen. The term flow spreader is commonly applied to apparatus developed for the purpose of effecting this transformation of fluid flow, and the device forming the opening through which the steam of stock is deposited on the screen is commonly referred to as a slice. Although the term stock utilized throughout this application designates cellulosic fibers dispersed in water, it is also intended to include any liquid system, whether or not containing fibers.

A common form of apparatus in this category may employ a feed distribution tube or header, which oftentimes is tapered, communicating with a plurality of laterals or branch tubes, spaced along the header and communicating at their opposite ends with a blending chamber, which is sometimes referred to as an explosion chamber." This flow spreading system functions to first divide a single large flow or stream of relatively low velocity into a plurality of higher velocity smaller flows or streams spaced along a common plane, which flows or streams are thereafter blended in flow passage means of the desired final width. Such systems are in widespread use in papermaking machines, but because prior systems have been more or less imperfect, it has been necessary to employ other means, such as deceleration chambers, rectifier rolls and flow boxes downstream of the flow spreader to achieve a truly uniform stream for papermaking purposes.

This invention embodies the concept of flow spreader design disclosed in our U.S. Pat. No. 3,298,905, issued Jan. 17, 1967 and entitled Tapered Manifold Type stock Distribu tor For a Papermaking Machine, which recognizes the existence of certain critical relationships between the dimensions and disposition of the several branch tubes and the configuration and dimensions of the blending chamber associated with these tubes. As a result of that invention, it is possible to construct flow spreading devices capable of producing a relatively wide fluid flow having a sufficiently uniform velocity profile to permit the flow of stock, for example, to vbe delivered directly from the flow spreader to a nozzle-type slice on a paper machine, thereby eliminating one or more elaborate flow evening devices heretofore employed between the flow spreader and the slice.

While the above arrangement makes possible the formation of a relatively wide flow having a substantially uniform velocity profile, aneven greater flow uniformity is desired. It is also desired to eliminate the need to accurately design the tapered feed distribution tube or header from which the stock is removed by the branch tubes in order to obtain uniform flow velocity from tube to tube. More preferably, it is desired to eliminate the need for any tapered feed distribution tube and to enable the use of a cylindrical non-tapered feed distribution tube in its place. This will greatly simplify the construction of such apparatus and eliminate costly engineering.

However, when non-tapered or improperly designed forms of stock feed pipes are employed with the flow spreader constructed according to U.S. Pat. No. 3,298,905, for example, one in the form of a cylinder having no taper, the velocities in the branch tubes appear to be quite different. Thus, the flow issuing from the branch tube connected to the downstream end of the feed pipe is much greater than the flow issuing from a preceding branch tube. This velocity difference in the branch tubes renders the flow in the blending chamber nonuniform. This is primarily due to the effect of pressure fluctuations between the streams issuing from the branch tubes and impinging off a surface in the blending chamber. Such pressure fluctuations are due to differing velocity or energy levels between the streams issuing from the branch tubes. The pressure fluctuations cause velocity variations within the blending chamber between adjacent streams. This results in the velocity component of the stock in the feed pipe having a reverse influence on the velocity profile of the stock flowing through the blending chamber so that the velocity of stock in the path of flow from the branch tube connected to the upstream end of the feed pipe is greater, as is well-known by those acquainted with the fluid mechanics art.

The chief object and advantage of the present invention is to provide apparatus for developing flow from a feed distribution tube or header into a relatively wide stream having a uniform velocity profile regardless of the particular configuration of the feed distribution tube.

It is a further object and advantage of the present invention to provide means for eliminating pressure fluctuations.

between the streams issuing from branch tubes into a blending chamber until the effect of their differing energy levels due to differing velocity components of fluid taken from different points along the stock delivery pipe has been eliminated.

SUMMARY OF THE INVENTION The invention provides apparatus for developing, in a relatively wide conduit, fluid flow having a substantially uniform velocity profile across the width of the conduit. The apparatus includes wall means defining a blending chamber associated with the conduit and co-extensive in width therewith, which wall means include substantially parallel, spaced-apart top and bottom walls an two substantially parallel, spaced-apart side walls defining a relatively wide flow path, and an end wall joining the top and bottom walls and the side walls. A plurality of branch tubes communicate with the blending chamber through one of the top or bottom walls and are adapted to introduce stock into the blending chamber. A plurality of barrier elements are disposed within the blending chamber between the center lines of adjoining tubes. The barrier elements extend between the top and bottom walls and from the end wall to a point along the flow path through the blending chamber at least beyond the center lines of the branch tubes. The barrier elements preferably have a streamlined configuration designed to attenuate lateral turbulence in the stock issuing from adjacent branch tubes. The branch tubes are preferably substantially uniformly spaced apart from one another in a generally parallel arrangement in a common plane. This plane is preferably, but not necessarily, perpendicular to the flow path through the blending chamber. In addition, it is preferable, although not essential, that the apparatus of the invention be constructed to incorporate the critical relationships set forth in U.S. Pat. No. 3,298,905 discussed above.

DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevation view, partially in section, of a paper making machine embodying this invention;

FIG. 2 is an end view, partially in section, of the flow spreader employed in the papermaking machine of FIG. 1; and

FIG. 3 is a schematic perspective view, partially in section, showing a portion of the flow spreader of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The papermaking machine illustrated in FIG. 1 is of the Fourdrinier type in which a traveling form wire 1 l is entrained over a breast roll 12. Papermaking stock, a mixture of water and cellulosic fibers, is deposited on the upper surface of the top run or wire 11 in such a manner that the water drains through, or is drawn through, the wire 11 and the fibers are retained on the wire 11 in the form of a damp web. Some machines are equipped with a breast roll which has cells 13 provided in the periphery thereof to facilitate drainage of water through the forming wire. The well-known process of removing the clamp paper web from the forming wire 11 and subsequently drying the web is performed by apparatus which is not shown in the drawing.

Forming wires 11 on papermaking machines may be up to 18 feet wide. If a machine is to produce a paper web of uniform thickness and appearance across its entire width, the stock delivered to the wire 11 must arrive in a stream which is flowing at an extremely uniform velocity across its width. Any variation in velocity across the width of the stream, and any cross-flow currents existing anywhere in the stream are likely to result in an uneven application of fibers to the wire 11 and the production ofa non-uniform paper web.

The stock delivery system for the papermaking machine in FIG. 1 includes a nozzle-type slice 14 extending nearly the full width of forming wire 11 and designed to deposit stock onto the wire 11 substantially tangentially of the path of travel of the wire and at a velocity approximating the velocity of the wire. Stock is conveyed to the vicinity of nozzle 14 from a remotely located pump (not shown) by means of a paper 16 which, for practical reasons, is generally circular in cross section. The relatively confined flow of stock in pipe 16 is transformed to the relatively wide and low height flow required for the nozzle 14 by means of a flow spreader, indicated generally by the reference numeral 17.

Spreader 17 includes a cylindrical non-tapered feed distributor tube, or header, l8 communicating at one end with delivery pipe 16. In accordance with conventional practice, the opposite end of header 18 may be blocked offor may communicate with a return pipe 19, as shown in phantom outline, through which a portion of the stock flow from pipe 16 may be recirculated to the stock mixing and pumping portion of the papermaking machine. The header 18 may alternatively have a tapered configuration along its length without effecting the operation of the apparatus of the present invention.

Extending away from the header 18 is a row of laterals, or branch tubes, 21 which communicate at their lower ends with upper regions of the header along the length of the header. As taught in U.S. Pat. No. 3,298,905, branch tubes 21, when used in conjunction with a properly designed tapered header, function to divide the stream of stock into a plurality of higher velocity flows which are substantially uniform from tube to tube. The row of tubes 21 extends for a distance only slightly less than the width of nozzle 14 so that a flow can be provided of sufficient width to supply the nozzle. However, where a cylindrical header 18 as shown is used, the flows through the branch tubes have differing velocity from tube to tube according to a well-known principle of fluid dynamics, with the higher velocity occurring in the branch tube connected to the header 18 further downstream.

In any event, blending of the individual flows from branch tubes 21 is effected in a blending chamber 22. It is a principal objective of this invention to provide a blending chamber 22 which is capable of developing a flow of sufficiently uniform velocity as to be deliverable directly to nozzle 14 by a simple connecting conduit 23. A particular feature of the blending chamber is its ability to reduce loss of energy from the streams from branch tubes 21 due to pressure fluctuations between streams. Although conduit 23 may be tapered slightly, as indicated in FIG. 1, in order to accelerate the stock flowing therethrough, additional flow evening devices, such as rectifier rolls and flow boxes are not required downstream of the flow spreader of this invention.

As indicated in FIGS. 1 to 3, blending chamber 22 is preferably rectangular in configuration and is bounded by substuntinlly flat und parallel top and bottom walls designated by numerals 24 and 25, respectively, parallel side walls 26, which are at right angles to top and bottom walls 24 and 25 and an end wall 27. End wall 27 is preferably disposed at right angles to the top and bottom walls as well as the side walls of the chamber. It will be noted that branch tubes 21 enter the bottom wall 25 of chamber 22 in a region of the chamber adjacent end wall 27, with the center lines of the tubes disposed approximately at right angles to walls 24 and 25 and parallel to end wall 27. The relationship preferably is such that the flow from each tube 21 is tangent to, or closely spaced from, end wall 27 of the chamber. However, the branch tubes 21 may enter the bottom wall 25 of chamber 22 at points spaced from the end wall 27 along the length of the flow path through the blending chamber 22 without adverse effects on the operation of the apparatus.

The stock discharged from tubes 21 impinges on the top wall 24 of blending chamber 22 and is deflected thereby, which characteristic is responsible for the term explosion chamber" being applied to this type of blending chamber. Although the entry of stock into chamber 22 does not involve an explosive action as such, the flow area in chamber 22 is somewhat greater than the combined flow areas of branch tubes 21 so that there is a consequent deceleration of the stock flow in the chamber 22.

In accordance with the invention, a plurality of barrier elements 30 are disposed in the blending chamber 22 between the center lines of adjoining branch tubes 21. These barrier elements 30 are shown in FIGS. 1, 2 and 3 of the drawings. The barrier elements 30 preferably have a streamlined configuration as shown in FIG. 3. Thus, the barrier elements 30 are tapered from their base adjacent end wall 27 to their downstream end. They have a relatively wide base which is affixed to the end wall 27 of the blending chamber 22.

The length of the barrier element 30 has been found to greatly influence its relative affect on fluid flow characteristics through the blending chamber 22. It has been found after considerable experimentation that the barrier elements should extend from the end wall 27 to a point at least beyond the center lines of the branch tubes 21 where they enter the blending chamber 22, and preferably to a point beyond the downstream side of the branch tubes 21 entering the blending chamber 22 through the bottom wall 25 shown in FIG. 3. The downstream side refers to the side of the branch tubes furthest along the flow path through the blending chamber 22. This insures that the barrier elements 30 will sufficiently isolate the streams entering the blending chamber 22 from adjacent branch tubes 21, so as to prevent pressure fluctuations primarily caused by differing energy levels or velocities of the streams impinged off of the inside surface of the top wall 24 of the blending chamber 22.

It is not necessary that the barrier elements 30 connect with the end wall 27. Thus, in instances where the end wall 27 is spaced from the upstream side of the branch tubes 21, the barrier elements 30 need only extend from a point preceding the upstream side of the branch tubes 21 to isolate the flow in separate streams.

Such impingement is desired to create widespread turbulence effects in a uniform manner across the width of the blending chamber 22 so as to discourage or prevent flocculation and to thoroughly diffuse the fibers in the stock carried by each of the streams. However, such pressure fluctuations create areas of flow separation and subsequent flow instability and this has been found to result in a local reduction of the flow velocity in the area of separation and instability and in the direction of the flow path through the blending chamber 22.

The fluid mechanics of impinging jets within a bounded region has been studied both experimentally and theoretically. It has been found that when two adjacent streams impinge on a plate within a blending chamber, a small zone of flow separation develops between the impinging jets. This separation zone extends along the back wall of the blending chamber between the adjacent streams, and continues for a short distance downstream until the steady fluid flow is re-established through the blending chamber. As the unsteady energy level of each adjacent stream changes, the location of the stagnation point oscillates along the back wall of the blending chamber, giving rise to pressure fluctuations between the streams. As a result, the size and location of the zone of separation is unsteady and this unsteadiness causes a reduction in flow efficiency. The most desirable boundary design which would eliminate this zone of separation is that geometrical form which most closely approximates the actual pattern of fluid motion. When a barrier element 30 is inserted between the two streams, it stablizes the location of the stagnation point on the surface of the barrier. Thus, when ideally contoured in a manner well-known to those skilled in the art,

the element 30 controls the location of the stagnation point and eliminates any separation zone. However, any barrier element 30 essentially eliminates pressure fluctuations between adjacent streams which may have unsteady energy levels.

The more serious problem which stems from the interaction of adjacent streams and the formation of pressure fluctuations is the tendency to form a velocity profile across the width of the blending chamber 22 which reflects to a varying degree pressure and velocity differences which exist in the stock flow pipe or header 18 or the branch tubes 21 connected along the length of the flow pipe or header 18 which remove stock therefrom at different pressures and velocities. As mentioned above, such pressure and velocity differences may show up in a given instance in a greatly magnified form such that small velocity differences between the flows in adjacent branch tubes become large velocity differences in adjacent areas of the blending chamber 22. The barrier elements 30 are so successful in preventing this pressure and velocity instability from being transferred to the flow path through the blending chamber 22, that it is no longer necessary to utilize a tapered stock flow pipe or header or to take any other design precautions to equalize flow velocity in the branch tubes 21 transferring stock from the header 18 to the blending chamber 22.

The barrier elements 30 preferably extend from the end wall 21 to a point along the flow path through the blending chamber 22 located not more than five times the diameter of one of the branch tubes downstream from the downstream side of the branch tubes. This is not a critical limitation, but if the barrier elements extend further than this distance along the flow path through the blending chamber 22, streaks may be formed in the resulting web. These streaks are formed by lines of reduced velocity caused by frictional flow resistance between the stock and the surface of the barrier elements 30. However, if a sufficiently long flow path is provided, these adverse effects are eliminated prior to deposition of the stock onto the forming wire 11 to form a paper web, and barrier elements 30 of greater length may be employed if desired.

A preferred embodiment of the apparatus of the invention possesses certain relationships between the flow area in the chamber 22 and the flow areas and disposition of branch tubes 21, as set forth in US. Pat. No. 3,298,905. However, it should be clearly understood that the incorporation of the barrier elements 30 into a blending chamber 22 in the manner described above makes possible the elimination of crossflows between streams entering the blending chamber 22 even when the form of apparatus is such that it does not possess the following relationships. These relationships are expressed in the following equation, which refers to dimensional factors depicted in FIG. 3 of the drawings.

-y =4SDI'n-d wherein y is a dimensionless ratio S is the distance between center lines of the branch tube 21, D is the depth ofthe blending chamber 22, and d is the diameter of the branch tubes 21.

It will be noted that the above equation 7 is an expression of the ratio of the incremental flow areas in the blending chamber 22 between center lines of branch tubes 22 (SD) to the flow areas of the branch tubes 22 ('rrd )/4. Obviously, if the apparatus under consideration employed laterals having cross sections other than circular, then the equation for 7 should be modified to reflect the flow area for the particular cross section used.

It has been determined that optimum production of uniform flow in blending chamber 22 can be achieved with a 'y value of approximately 1.5 and that results superior to prior flow spreading devices of this character can be achieved when 7 is maintained within the range of from about 1.1 to about 1.7.

Maintaining the dimensionless ratio 7 within the range given above produces the most desirable results when the space (S) between the center lines of branch tubes 21 is approximately 2.4 times the diameter (d) of the branch tubes. This spacing relationship is in accordance with good design practice for multiple passage flow spreaders utilizing manifolds, such as manifold 18, and provides sufficient spacing for incorporation of such fittings and welds as may be required for economical fabrication of the flow spreader. However, it has been determined that minor departures from an S/d ratio of 2.4, whether increasing or decreasing the ratio, have little bearing on the validity of the 'y relationship and range above described and even major departures can be made in the direction of a decreasing ratio without adversely affecting performance of the flow spreader.

It is generally considered unwise to increase the spacing of the branch tubes 21 to a distance much greater than 2% times the diameter of the tubes because this results in fewer tubes being available to convey fluid to the blending chamber 22 with a consequent increase in the velocity of flow in the individual tubes.

A practical design approach in laying out a flow spreading device incorporating these characteristics will generally involve first selecting those dimensions for the branch tubes 21 and their spacing (S) which in cooperation with the header 18 provide the most uniform distribution of flow among the branch tubes at the desired rate of flow. As stated previously, this will generally result in an S/d ratio of approximately 2.4. Thereafter, a dimension for the depth (D) of blending chamber 22 is selected which when substituted in the above equation together with the values of S and D give a 7 value falling within the desired range.

Flow in blending chamber 22 is preferably maintained at Reynolds numbers in excess of 10,000 to maintain turbulent flow conditions through the chamber, as well as through delivery conduit 23 and into the nozzle 14.

In one flow spreading device constructed in accordance with this invention, a rectangular blending chamber 22 having a width of 20 inches and a depth of 0.531 inches was fed from a row of 9 branch tubes 21 of 1.049 inches inside diameter each, arranged with 2.219 inches center line spacing. The branch tubes 21 were connected to a cylindrical non-tapered header 18 having one closed end, a length of 20 inches and an inside diameter of 4 inches, at 2.219 inches center line spacing. The relative disposition of the branch tubes 21 with respect to the walls of the blending chamber 22 was essentially the same as that illustrated in the drawings. The ratio 7 calculated in accordance with the above equation was 1.36.

Average velocity is calculated from discharge measurements taken at the outlets of the branch tubes when the blending chamber was not attached revealed a maximum variation between branch tubes of about 9 percent, being higher at the branch tube connected furthest downstream to the header. With the blending chamber attached, velocity measurements taken across the outlet of the blending chamber, located at a point 32 inches from the plane of the center lines of the branch tubes or 60 times the dimension D" equal to 0.531 inch, at stations spaced apart by distances equivalent to onehalf of the center line spacing of the branch tubes revealed a maximum variation in the velocity profile of 28 percent, being higher at the station in the path of flow from the branch tube connected to the upstream end of the header. Thus, the blending chamber surprisingly reversed the velocity profile and, in addition, greatly magnified the velocity differences existing between the adjacent branch tubes.

TABLE Distance From End Wall (whcre upstream side of Percentage Variation from average velocity branch tube is tangent ofthe profile with end wall] inches 28 k 0.25 inches 20.5% 0.50 inches 6.0% L0 inches 2.0 inches 3.5% 5.0 inches 5.5% 8.0 inches 9.0%

l2.0 inches 13.5%

The above results clearly indicate that barrier elements extending downstream in the blending chamber at least beyond the center lines of the branch tubes and up to a multiple offive times the diameter of the branch tubes beyond the downstream side of the branch tubes results in a substantially uniform flow velocity profile. In view of the fact that the nonuniform tlow resulting from a cylindrical non-tapered header can be improved to the extent shown above, it is readily apparent that an even more uniform velocity profile can be obtained when a tapered header is utilized to eliminate the great difference initially existing in the velocity profile through the blending chamber prior to the insertion of the barrier elements 30.

The effectiveness of blending chamber 22 is, of course, influenced to a degree by the length of the chamber (indicated by letter L in FIG. 3) as some distance of flow must be provided for complete blending of the individual flows from branch tubes 21 and beyond the downstream ends of barrier elements 30. It has been found that a blending chamber constructed in accordance with the principles set forth above permits uniform blending of the flow across the width (W) of the blending chamber in a shorter distance than was heretofore believed to be practicable. In general, when the dimensionless ratio 7 is maintained in the range set forth above, the length (L) of the blending chamber may be as low as 25 times the depth (D) of the chamber. Consequently, with this invention it is possible to construct a stock delivery system for a paper machine which occupies a minimum amount of space at the head, or wet, end of the machine. The above ratios may change slightly where barrier elements are employed which extend further downstream through the blending chamber.

Although, in the papermaking machine illustrated in the drawings, the branch tubes 21 direct their individual flows upwardly into blending chamber 22 through the bottom wall 25 of the chamber, it is to be understood that this attitude of the system is not essential to proper functioning of the blending chamber 22 or of the flow spreader generally. The system could be inverted, for example, with branch tubes 21 directed through the top wall 24 of the blending chamber 22. I

One of the desirable features of this invention is the simplicity of construction of the blending chamber portion of the flow spreader 17. The box-like configuration for blending chamber 22 permits this portion of the flow spreader to be fabricated from metal sheet or plate, or other flat material, with an absolute minimum of shaping, drilling, and forming. The barrier elements may be advantageously formed integrally with the end wall in certain instances, such as where the barrier elements are to be tapered or contoured as by molding. Moreover, it is not essential to the practice of this invention that the opposing walls forming blending chamber 22 be absolutely planar and/or parallel because beneficial results can be obtained even if minor departures from the relationship shown and described are dictated by other design considerations.

Similarly, the flow through branch tubes 21 need not necessarily enter the blending chamber 22 in the precise manner shown and described. Although it is preferable to have fluid enter blending chamber 22 at and parallel to the end wall 27 of the chamber, spacing the end wall rearwardly from tubes 21 by a small amount as mentioned above will not adversely affect operation of of the flow spreader.

As mentioned above, a further desirable feature of this invention resides in-the elimination of the need to design the header 18 to compensate for flow velocity variations among the several branch tubes 21, that is, to counteract the tendency for the velocity of flow in the tubes connected to the downstream end of the header to be greater than the velocity in the tubes connected to the upstream end of the header. A blending chamber 22 having barrier elements 30 in accordance with this invention eliminates the need to utilize a tapered header at all and makes it possible to utilize a cylindrical non-tapered header in the form of a straight pipe with the attendant cost savings.

The efficiency of the flow spreader of this invention, which, as mentioned previously, eliminates the necessity for employing additional flow evening devices, also eliminates the operational hazards commonly associated with deceleration devices, such as a tendency toward flocculation of the papermaking fibers, the development of slime and the plugging of flow passages. Furthermore, the flow spreader of this invention has very low energy losses associated therewith.

Although the elimination of supplementary flow evening devices and a tapered header is one of the principal advantages to be gained through utilization of the flow spreading system of this invention, it is to be understood that the use of this flow spreader need not necessarily be exclusive of such supplementary devices. For example, there may be instances in which the flow spreader of this invention can be incorporated into an existing papermaking machine wherein, for reasons of economy, it is not desired to remove an existing headbox and associated equipment. Incorporation of the flow spreader of this invention into such an existing system should, nevertheless, permit the flow evening capabilities of the spreader to be taken advantage of in improving overall performance of the stock delivery system.

We claim:

1. Apparatus for developing, in a relatively wide conduit, fluid flow having a substantially uniform velocity profile across the width of the conduit, comprising wall means defining a blending chamber associated with said conduit, said wall means including substantially parallel, spaced-apart top and bottom walls and two substantially parallel, spaced-apart side walls defining a relatively wide flow path, and an end wall joining said top and bottom walls and said side walls,

a plurality of branch tubes communicating with said blending chamber through one of said top or bottom walls and being adapted to introduce stock into said blending chamber, and

a plurality of barrier elements disposed within said blending chamber between the center lines of adjoining tubes, said barrier elements extending between said top and bottom walls and from a point preceding the upstream side of said branch tubes to a point along the flow path through said blending chamber at least beyond the center lines of said branch tubes.

2. Apparatus according to claim 1, wherein said barrier elements have a streamlined configuration designed to eliminate separation and resultant instability in the stock issuing from adjacent branch tubes.

3. Apparatus according to claim 1, wherein said branch tubes are substantially uniformly spaced-apart from one another in a generally parallel arrangement in a common plane.

4. Apparatus according to claim 3, wherein said barrier elements extend from said end wall to a point along the flow path through said blending chamber at least beyond the center lines of said branch tubes.

5. Apparatus according to claim 4, wherein said barrier elements extend from said end wall to a point along the flow path through said blending chamber at least beyond the downstream side of said branch tubes.

6. Apparatus according to claim 4, wherein said barrier elements extend from said end wall to a point along the flow path downstream therefrom by a distance of up to five times the diameter of one of said branch tubes.

8. Apparatus according to claim 4, wherein said branch tubes are of substantially equal in diameter and communicate with said blending chamber through one of said sidewalls at a point adjacent said end wall, and wherein said barrier elements extend from said end wall for a distance along the flow path through said blending chamber equal to a multiple of the diameter of said branch tubes of between about 1 and 1.5.

9. Apparatus according to claim 4, wherein the ratio of the flow area in said blending chamber between center lines of ad jacent branch tubes measured in said center line plane to the flow area in each of said branch tubes is in the range of from about 1.1 to about 1.7.

10. Apparatus according to claim 9, wherein said ratio is approximately 1.5.

11. Apparatus according to claim 4, wherein said apparatus satisfies the following equation: y=4SD/1rd wherein:

S- is the distance between center lines of said tubes,

D- is the distance between said top and bottom walls,

dis the diameter of said tubes,

7- is from about 1.1 to about 1.7.

12. Apparatus according to claim 11 wherein -y is approximately 1.5.

13. ln a papermaking apparatus comprising a stock delivery pipe,

a plurality of branch tubes communicating with said pipe for dividing at least a portion of the stock flow in each pipe into a plurality of higher velocity, smaller volume flows, said tubes being substantially uniformly-spaced-apart in parallel arrangement in a common plane,

means defining a blending chamber communicating with said tubes, said blending chamber being of boxlike configuration and disposed to receive stock from said tubes through one wall thereof in a flow direction normal to the opposite wall of said chamber, and

slice means communicating with said blending chamber,

the improvement comprising a plurality of barrier elements disposed within said blending chamber between the center lines of adjoining tubes, said barrier elements extending between said walls of said means and extending from a point preceding the upstream side of said branch tubes to a point along the flow path through said blending chamber at least beyond the center lines of said branch tubes.

14. The improvement in papermaking apparatus according to claim 13, wherein said means defining a blending chamber include an end wall connecting top and bottom walls, and said barrier elements extend between said top and bottom walls and from said end wall to a point along the flow path through said blending chamber at least beyond the center lines of said branch tubes. l 

1. Apparatus for developing, in a relatively wide conduit, fluid flow having a substantially uniform velocity profile across the width of the conduit, comprising wall means defining a blending chamber associated with said conduit, said wall means including substantially parallel, spaced-apart top and bottom walls and two substantially parallel, spaced-apart side walls defining a relatively wide flow path, and an end wall joining said top and bottom walls and said side walls, a plurality of branch tubes communicating with said blending chamber through one of said top or bottom walls and being adapted to introduce stock into said blending chamber, and a plurality of barrier elements disposed within said blending chamber between the center lines of adjoining tubes, said barrier elements extending between said top and bottom walls and from a point preceding the upstream side of said branch tubes to a point along the flow path through said blending chamber at least beyond the center lines of said branch tubes.
 2. Apparatus according to claim 1, wherein said barrier elements have a streamlined configuration designed to eliminate separation and resultant instability in the stock issuing from adjacent branch tubes.
 3. Apparatus according to claim 1, wherein said branch tubes are substantially uniformly spaced-apart from one another in a generally parallel arrangement in a common plane.
 4. Apparatus according to claim 3, wherein said barrier elements extend from said end wall to a point along the flow path through said blending chamber at least beyond the center lines of said branch tubes.
 5. Apparatus according to claim 4, wherein said barrier elements extend from said end wall to a point along the flow path through said blending chamber at least beyond the downstream side of said branch tubes.
 6. Apparatus according to claim 4, wherein said barrier elements extend from said end wall to a point along the flow path through said blending chamber between the downstream side of said branch tubes and a point spaced downstream therefrom by a distance of up to five times the diameter of one of said branch tubes.
 7. Apparatus according to claim 4, wherein said branch tubes are substantially equal in diameter, and wherein said barrier elements extend from said end wall to a point along the flow path through said blending chamber between the Downstream side of said branch tubes and a point spaced downstream therefrom by a distance of up to five times the diameter of one of said branch tubes.
 8. Apparatus according to claim 4, wherein said branch tubes are of substantially equal in diameter and communicate with said blending chamber through one of said sidewalls at a point adjacent said end wall, and wherein said barrier elements extend from said end wall for a distance along the flow path through said blending chamber equal to a multiple of the diameter of said branch tubes of between about 1 and 1.5.
 9. Apparatus according to claim 4, wherein the ratio of the flow area in said blending chamber between center lines of adjacent branch tubes measured in said center line plane to the flow area in each of said branch tubes is in the range of from about 1.1 to about 1.7.
 10. Apparatus according to claim 9, wherein said ratio is approximately 1.5.
 11. Apparatus according to claim 4, wherein said apparatus satisfies the following equation: gamma 4SD/ pi d2 wherein: S- is the distance between center lines of said tubes, D- is the distance between said top and bottom walls, d- is the diameter of said tubes, gamma - is from about 1.1 to about 1.7.
 12. Apparatus according to claim 11 wherein gamma is approximately 1.5.
 13. In a papermaking apparatus comprising a stock delivery pipe, a plurality of branch tubes communicating with said pipe for dividing at least a portion of the stock flow in each pipe into a plurality of higher velocity, smaller volume flows, said tubes being substantially uniformly spaced apart in parallel arrangement in a common plane, means defining a blending chamber communicating with said tubes, said blending chamber being of box-like configuration and disposed to receive stock from said tubes through one wall thereof in a flow direction normal to the opposite wall of said chamber, and slice means communicating with said blending chamber, the improvement comprising a plurality of barrier elements disposed within said blending chamber between the center lines of adjoining tubes, said barrier elements extending between said walls of said means and extending from a point preceding the upstream side of said branch tubes to a point along the flow path through said blending chamber at least beyond the center lines of said branch tubes.
 14. The improvement in papermaking apparatus according to claim 13, wherein said means defining a blending chamber include an end wall connecting top and bottom walls, and said barrier elements extend between said top and bottom walls and from said end wall to a point along the flow path through said blending chamber at least beyond the center lines of said branch tubes. 